Short latency fast retransmission triggering

ABSTRACT

The invention relates to an improved transmission protocol for uplink data packet transmission in a communication system. A receiver of a user equipment receives a Fast Retransmission Indicator, referred to as FRI. The FRI indicates whether or not a base station requests a retransmission of a previously transmitted data packet. A transmitter of the user equipment retransmits the data packet using the same redundancy version as already used for the previous transmission of the data packet.

BACKGROUND Technical Field

The present disclosure relates to methods for operating a transmissionprotocol for uplink data packet transmission in a communication system.The present disclosure is also providing the user equipment and basestation for participating in the methods described herein.

Description of the Related Art

Long Term Evolution (LTE)

Third-generation mobile systems (3G) based on WCDMA radio-accesstechnology are being deployed on a broad scale all around the world. Afirst step in enhancing or evolving this technology entails introducingHigh-Speed Downlink Packet Access (HSDPA) and an enhanced uplink, alsoreferred to as High Speed Uplink Packet Access (HSUPA), giving a radioaccess technology that is highly competitive.

In order to be prepared for further increasing user demands and to becompetitive against new radio access technologies, 3GPP introduced a newmobile communication system which is called Long Term Evolution (LTE).LTE is designed to meet the carrier needs for high speed data and mediatransport as well as high capacity voice support for the next decade.The ability to provide high bit rates is a key measure for LTE.

The work item (WI) specification on Long-Term Evolution (LTE) calledEvolved UMTS Terrestrial Radio Access (UTRA) and UMTS Terrestrial RadioAccess Network (UTRAN) is finalized as Release 8 (LTE Rel. 8). The LTEsystem represents efficient packet-based radio access and radio accessnetworks that provide full IP-based functionalities with low latency andlow cost. In LTE, scalable multiple transmission bandwidths arespecified such as 1.4, 3.0, 5.0, 10.0, 15.0, and 20.0 MHz, in order toachieve flexible system deployment using a given spectrum. In thedownlink, Orthogonal Frequency Division Multiplexing (OFDM)-based radioaccess was adopted because of its inherent immunity to multipathinterference (MPI) due to a low symbol rate, the use of a cyclic prefix(CP) and its affinity to different transmission bandwidth arrangements.Single-carrier frequency division multiple access (SC-FDMA)-based radioaccess was adopted in the uplink, since provisioning of wide areacoverage was prioritized over improvement in the peak data rateconsidering the restricted transmit power of the user equipment (UE).Many key packet radio access techniques are employed includingmultiple-input multiple-output (MIMO) channel transmission techniques,and a highly efficient control signaling structure is achieved in LTERel. 8/9.

LTE Architecture

The overall LTE architecture is shown in FIG. 1 . The E-UTRAN consistsof an eNodeB, providing the E-UTRA user plane (PDCP/RLC/MAC/PHY) andcontrol plane (RRC) protocol terminations towards the user equipment(UE). The eNodeB (eNB) hosts the Physical (PHY), Medium Access Control(MAC), Radio Link Control (RLC) and Packet Data Control Protocol (PDCP)layers that include the functionality of user-plane header compressionand encryption. It also offers Radio Resource Control (RRC)functionality corresponding to the control plane. It performs manyfunctions including radio resource management, admission control,scheduling, enforcement of negotiated uplink Quality of Service (QoS),cell information broadcast, ciphering/deciphering of user and controlplane data, and compression/decompression of downlink/uplink user planepacket headers. The eNodeBs are interconnected with each other by meansof the X2 interface.

The eNodeBs are also connected by means of the S1 interface to the EPC(Evolved Packet Core), more specifically to the MME (Mobility ManagementEntity) by means of the S1-MME and to the Serving Gateway (SGW) by meansof the S1-U. The S1 interface supports a many-to-many relation betweenMMEs/Serving Gateways and eNodeBs. The SGW routes and forwards user datapackets, while also acting as the mobility anchor for the user planeduring inter-eNodeB handovers and as the anchor for mobility between LTEand other 3GPP technologies (terminating S4 interface and relaying thetraffic between 2G/3G systems and PDN GW). For idle-state userequipments, the SGW terminates the downlink data path and triggerspaging when downlink data arrives for the user equipment. It manages andstores user equipment contexts, e.g., parameters of the IP bearerservice, or network internal routing information. It also performsreplication of the user traffic in case of lawful interception.

The MME is the key control-node for the LTE access-network. It isresponsible for idle-mode user equipment tracking and paging procedureincluding retransmissions. It is involved in the beareractivation/deactivation process and is also responsible for choosing theSGW for a user equipment at the initial attach and at the time ofintra-LTE handover involving Core Network (CN) node relocation. It isresponsible for authenticating the user (by interacting with the HSS).The Non-Access Stratum (NAS) signaling terminates at the MME, and it isalso responsible for the generation and allocation of temporaryidentities to user equipments. It checks the authorization of the userequipment to camp on the service provider's Public Land Mobile Network(PLMN) and enforces user equipment roaming restrictions. The MME is thetermination point in the network for ciphering/integrity protection forNAS signaling and handles the security key management. Lawfulinterception of signaling is also supported by the MME. The MME alsoprovides the control plane function for mobility between LTE and 2G/3Gaccess networks with the S3 interface terminating at the MME from theSGSN. The MME also terminates the S6a interface towards the home HSS forroaming user equipments.

Component Carrier Structure in LTE

The downlink component carrier of a 3GPP LTE system is subdivided in thetime-frequency domain in so-called subframes. In 3GPP LTE each subframeis divided into two downlink slots as shown in FIG. 2 , wherein thefirst downlink slot comprises the control channel region (PDCCH region)within the first OFDM symbols. Each subframe consists of a give numberof OFDM symbols in the time domain (12 or 14 OFDM symbols in 3GPP LTE(Release 8)), wherein each OFDM symbol spans over the entire bandwidthof the component carrier. The OFDM symbols thus each consist of a numberof modulation symbols transmitted on respective subcarriers. In LTE, thetransmitted signal in each slot is described by a resource grid ofN_(RB) ^(DL)N_(sc) ^(RB) subcarriers and N_(symb) ^(DL) OFDM symbols.N_(RB) ^(DL) is the number of resource blocks within the bandwidth. Thequantity N_(RB) ^(DL) depends on the downlink transmission bandwidthconfigured in the cell and shall fulfill N_(RB) ^(min,DL)≤N_(RB)^(DL)≤N_(RB) ^(max,DL), where N_(RB) ^(min,DL)=6 and N_(RB)^(max,DL)=110 are respectively the smallest and the largest downlinkbandwidths, supported by the current version of the specification.N_(sc) ^(RB) is the number of subcarriers within one resource block. Fornormal cyclic prefix subframe structure, N_(sc) ^(RB)=12 and N_(symb)^(DL)=7.

Assuming a multi-carrier communication system, e.g., employing OFDM, asfor example used in 3GPP Long Term Evolution (LTE), the smallest unit ofresources that can be assigned by the scheduler is one “resource block.”A physical resource block (PRB) is defined as consecutive OFDM symbolsin the time domain (e.g., 7 OFDM symbols) and consecutive subcarriers inthe frequency domain as exemplified in FIG. 2 (e.g., 12 subcarriers fora component carrier). In 3GPP LTE (Release 8), a physical resource blockthus consists of resource elements, corresponding to one slot in thetime domain and 180 kHz in the frequency domain (for further details onthe downlink resource grid, see for example 3GPP TS 36.211, “EvolvedUniversal Terrestrial Radio Access (E-UTRA); Physical Channels andModulation (Release 8),” current version 13.0.0, section 6.2, availableat http://www.3gpp.org and incorporated herein by reference).

One subframe consists of two slots, so that there are 14 OFDM symbols ina subframe when a so-called “normal” CP (cyclic prefix) is used, and 12OFDM symbols in a subframe when a so-called “extended” CP is used. Forsake of terminology, in the following the time-frequency resourcesequivalent to the same consecutive subcarriers spanning a full subframeis called a “resource block pair,” or equivalent “RB pair” or “PRBpair.”

The term “component carrier” refers to a combination of several resourceblocks in the frequency domain. In future releases of LTE, the term“component carrier” is no longer used; instead, the terminology ischanged to “cell,” which refers to a combination of downlink andoptionally uplink resources. The linking between the carrier frequencyof the downlink resources and the carrier frequency of the uplinkresources is indicated in the system information transmitted on thedownlink resources.

Similar assumptions for the component carrier structure will apply tolater releases too.

Carrier Aggregation in LTE-A for Support of Wider Bandwidth

The frequency spectrum for IMT-Advanced was decided at the World Radiocommunication Conference 2007 (WRC-07). Although the overall frequencyspectrum for IMT-Advanced was decided, the actual available frequencybandwidth is different according to each region or country. Followingthe decision on the available frequency spectrum outline, however,standardization of a radio interface started in the 3rd GenerationPartnership Project (3GPP). At the 3GPP TSG RAN #39 meeting, the StudyItem description on “Further Advancements for E-UTRA (LTE-Advanced)” wasapproved. The study item covers technology components to be consideredfor the evolution of E-UTRA, e.g., to fulfill the requirements onIMT-Advanced.

The bandwidth that the LTE-Advanced system is able to support is 100MHz, while an LTE system can only support 20 MHz. Nowadays, the lack ofradio spectrum has become a bottleneck of the development of wirelessnetworks, and as a result it is difficult to find a spectrum band whichis wide enough for the LTE-Advanced system. Consequently, it is urgentto find a way to gain a wider radio spectrum band, wherein a possibleanswer is the carrier aggregation functionality.

In carrier aggregation, two or more component carriers are aggregated inorder to support wider transmission bandwidths up to 100 MHz. Severalcells in the LTE system are aggregated into one wider channel in theLTE-Advanced system which is wide enough for 100 MHz even though thesecells in LTE may be in different frequency bands.

All component carriers can be configured to be LTE Rel. 8/9 compatible,at least when the bandwidth of a component carrier does not exceed thesupported bandwidth of an LTE Rel. 8/9 cell. Not all component carriersaggregated by a user equipment may necessarily be Rel. 8/9 compatible.Existing mechanisms (e.g., barring) may be used to avoid Rel-8/9 userequipments to camp on a component carrier.

A user equipment may simultaneously receive or transmit on one ormultiple component carriers (corresponding to multiple serving cells)depending on its capabilities. An LTE-A Rel. 10 user equipment withreception and/or transmission capabilities for carrier aggregation cansimultaneously receive and/or transmit on multiple serving cells,whereas an LTE Rel. 8/9 user equipment can receive and transmit on asingle serving cell only, provided that the structure of the componentcarrier follows the Rel. 8/9 specifications.

Carrier aggregation is supported for both contiguous and non-contiguouscomponent carriers with each component carrier limited to a maximum of110 Resource Blocks in the frequency domain (using the 3GPP LTE (Release8/9) numerology).

It is possible to configure a 3GPP LTE-A (Release 10)-compatible userequipment to aggregate a different number of component carriersoriginating from the same eNodeB (base station) and of possiblydifferent bandwidths in the uplink and the downlink. The number ofdownlink component carriers that can be configured depends on thedownlink aggregation capability of the UE. Conversely, the number ofuplink component carriers that can be configured depends on the uplinkaggregation capability of the UE. It may currently not be possible toconfigure a mobile terminal with more uplink component carriers thandownlink component carriers. In a typical TDD deployment the number ofcomponent carriers and the bandwidth of each component carrier in uplinkand downlink is the same. Component carriers originating from the sameeNodeB need not provide the same coverage.

The spacing between center frequencies of contiguously aggregatedcomponent carriers shall be a multiple of 300 kHz. This is in order tobe compatible with the 100 kHz frequency raster of 3GPP LTE (Release8/9) and at the same time to preserve orthogonality of the subcarrierswith 15 kHz spacing. Depending on the aggregation scenario, the n×300kHz spacing can be facilitated by insertion of a low number of unusedsubcarriers between contiguous component carriers.

The nature of the aggregation of multiple carriers is only exposed up tothe MAC layer. For both uplink and downlink there is one HARQ entityrequired in MAC for each aggregated component carrier. There is (in theabsence of SU-MIMO for uplink) at most one transport block per componentcarrier. A transport block and its potential HARQ retransmissions needto be mapped on the same component carrier.

When carrier aggregation is configured, the mobile terminal only has oneRRC connection with the network. At RRC connectionestablishment/re-establishment, one cell provides the security input(one ECGI, one PCI and one ARFCN) and the non-access stratum mobilityinformation (e.g., TAI) similarly as in LTE Rel. 8/9. After RRCconnection establishment/re-establishment, the component carriercorresponding to that cell is referred to as the downlink Primary Cell(PCell). There is always one and only one downlink PCell (DL PCell) andone uplink PCell (UL PCell) configured per user equipment in connectedstate. Within the configured set of component carriers, other cells arereferred to as Secondary Cells (SCells); with carriers of the SCellbeing the Downlink Secondary Component Carrier (DL SCC) and UplinkSecondary Component Carrier (UL SCC). Maximum five serving cells,including the PCell, can be configured for one UE.

MAC Layer/Entity, RRC Layer, Physical Layer

The LTE layer 2 user-plane/control-plane protocol stack comprises foursublayers, RRC, PDCP, RLC and MAC. The Medium Access Control (MAC) layeris the lowest sublayer in the Layer 2 architecture of the LTE radioprotocol stack and is defined by e.g., the 3GPP technical standard TS36.321, current version 13.0.0. The connection to the physical layerbelow is through transport channels, and the connection to the RLC layerabove is through logical channels. The MAC layer therefore performsmultiplexing and demultiplexing between logical channels and transportchannels: the MAC layer in the transmitting side constructs MAC PDUs,known as transport blocks, from MAC SDUs received through logicalchannels, and the MAC layer in the receiving side recovers MAC SDUs fromMAC PDUs received through transport channels.

The MAC layer provides a data transfer service (see subclauses 5.4 and5.3 of TS 36.321 incorporated herein by reference) for the RLC layerthrough logical channels, which are either control logical channelswhich carry control data (e.g., RRC signaling) or traffic logicalchannels which carry user plane data. On the other hand, the data fromthe MAC layer is exchanged with the physical layer through transportchannels, which are classified as downlink or uplink. Data ismultiplexed into transport channels depending on how it is transmittedover the air.

The Physical layer is responsible for the actual transmission of dataand control information via the air interface, i.e., the Physical Layercarries all information from the MAC transport channels over the airinterface on the transmission side. Some of the important functionsperformed by the Physical layer include coding and modulation, linkadaptation (AMC), power control, cell search (for initialsynchronization and handover purposes) and other measurements (insidethe LTE system and between systems) for the RRC layer. The Physicallayer performs transmissions based on transmission parameters, such asthe modulation scheme, the coding rate (i.e., the modulation and codingscheme, MCS), the number of physical resource blocks etc. Moreinformation on the functioning of the physical layer can be found in the3GPP technical standard 36.213 current version 13.0.0, incorporatedherein by reference.

The Radio Resource Control (RRC) layer controls communication between aUE and an eNB at the radio interface and the mobility of a UE movingacross several cells. The RRC protocol also supports the transfer of NASinformation. For UEs in RRC_IDLE, RRC supports notification from thenetwork of incoming calls. RRC connection control covers all proceduresrelated to the establishment, modification and release of an RRCconnection, including paging, measurement configuration and reporting,radio resource configuration, initial security activation, andestablishment of Signaling Radio Bearer (SRBs) and of radio bearerscarrying user data (Data Radio Bearers, DRBs).

The radio link control (RLC) sublayer comprises mainly ARQ functionalityand supports data segmentation and concatenation, i.e., RLC layerperforms framing of RLC SDUs to put them into the size indicated by theMAC layer. The latter two minimize the protocol overhead independentlyfrom the data rate. The RLC layer is connected to the MAC layer vialogical channels. Each logical channel transports different types oftraffic. The layer above RLC layer is typically the PDCP layer, but insome cases it is the RRC layer, i.e., RRC messages transmitted on thelogical channels BCCH (Broadcast Control Channel), PCCH (Paging ControlChannel) and CCCH (Common Control Channel) do not require securityprotection and thus go directly to the RLC layer, bypassing the PDCPlayer. The main services and functions of the RLC sublayer include:

-   -   Transfer of upper layer PDUs supporting AM, UM or TM data        transfer;    -   Error Correction through ARQ;    -   Segmentation according to the size of the TB;    -   Resegmentation when necessary (e.g., when the radio quality,        i.e., the supported TB size changes)    -   Concatenation of SDUs for the same radio bearer is FFS;    -   In-sequence delivery of upper layer PDUs;    -   Duplicate Detection;    -   Protocol error detection and recovery;    -   SDU discard;    -   Reset

The ARQ functionality provided by the RLC layer will be discussed inmore detail at a later part.

Uplink Access Scheme for LTE

For uplink transmission, power-efficient user-terminal transmission isnecessary to maximize coverage. Single-carrier transmission combinedwith FDMA with dynamic bandwidth allocation has been chosen as theevolved UTRA uplink transmission scheme. The main reason for thepreference for single-carrier transmission is the lower peak-to-averagepower ratio (PAPR), compared to multi-carrier signals (OFDMA), and thecorresponding improved power-amplifier efficiency and improved coverage(higher data rates for a given terminal peak power). During each timeinterval, eNodeB assigns users a unique time/frequency resource fortransmitting user data, thereby ensuring intra-cell orthogonality. Anorthogonal access in the uplink promises increased spectral efficiencyby eliminating intra-cell interference. Interference due to multipathpropagation is handled at the base station (eNode B), aided by insertionof a cyclic prefix in the transmitted signal.

The basic physical resource used for data transmission consists of afrequency resource of size BWgrant during one time interval, e.g., asubframe, onto which coded information bits are mapped. It should benoted that a subframe, also referred to as transmission time interval(TTI), is the smallest time interval for user data transmission. It ishowever possible to assign a frequency resource BWgrant over a longertime period than one TTI to a user by concatenation of subframes.

Layer 1/Layer 2 Control Signaling

In order to inform the scheduled users about their allocation status,transport format and other data related information (e.g., HARQ) L1/L2control signaling needs to be transmitted on the downlink along with thedata. The control signaling needs to be multiplexed with the downlinkdata in a sub frame (assuming that the user allocation can change fromsub frame to sub frame). Here, it should be noted, that user allocationmight also be performed on a TTI (Transmission Time Interval) basis,where the TTI length is a multiple of the sub frames. The TTI length maybe fixed in a service area for all users, may be different for differentusers, or may even by dynamic for each user. Generally, then the L1/2control signaling needs only be transmitted once per TTI. The L1/L2control signaling is transmitted on the Physical Downlink ControlChannel (PDCCH). It should be noted that assignments for uplink datatransmissions, UL grants, are also transmitted on the PDCCH.

In the following the detailed L1/L2 control signaling informationsignaled for DL allocation respectively uplink assignments is describedin the following:

Downlink Data Transmission

Along with the downlink packet data transmission, L1/L2 controlsignaling is transmitted on a separate physical channel (PDCCH). ThisL1/L2 control signaling typically contains information on:

-   -   The physical resource(s) on which the data is transmitted (e.g.,        subcarriers or subcarrier blocks in case of OFDM, codes in case        of CDMA). This information allows the UE (receiver) to identify        the resources on which the data is transmitted.    -   The transport Format, which is used for the transmission. This        can be the transport block size of the data (payload size,        information bits size), the MCS (Modulation and Coding Scheme)        level, the Spectral Efficiency, the code rate, etc. This        information (usually together with the resource allocation)        allows the UE (receiver) to identify the information bit size,        the modulation scheme and the code rate in order to start the        demodulation, the de rate matching and the decoding process. In        some cases the modulation scheme maybe signaled explicitly.    -   Hybrid ARQ (HARD) information:        -   Process number: Allows the UE to identify the hybrid ARQ            process on which the data is mapped        -   Sequence number or new data indicator: Allows the UE to            identify if the transmission is a new packet or a            retransmitted packet        -   Redundancy and/or constellation version: Tells the UE, which            hybrid ARQ redundancy version is used (required for de-rate            matching) and/or which modulation constellation version is            used (required for demodulation)    -   UE Identity (UE ID): Tells for which UE the L1/L2 control        signaling is intended for. In typical implementations this        information is used to mask the CRC of the L1/L2 control        signaling in order to prevent other UEs to read this        information.

Uplink Data Transmission

To enable an uplink packet data transmission, L1/L2 control signaling istransmitted on the downlink (PDCCH) to tell the UE about thetransmission details. This L1/L2 control signaling typically containsinformation on:

-   -   The physical resource(s) on which the UE should transmit the        data (e.g., subcarriers or subcarrier blocks in case of OFDM,        codes in case of CDMA).    -   The transport Format, the UE should use for the transmission.        This can be the transport block size of the data (payload size,        information bits size), the MCS (Modulation and Coding Scheme)        level, the Spectral Efficiency, the code rate, etc. This        information (usually together with the resource allocation)        allows the UE (transmitter) to pick the information bit size,        the modulation scheme and the code rate in order to start the        modulation, the rate matching and the encoding process. In some        cases the modulation scheme maybe signaled explicitly.    -   Hybrid ARQ information:        -   Process number: Tells the UE from which hybrid ARQ process            it should pick the data        -   Sequence number or new data indicator: Tells the UE to            transmit a new packet or to retransmit a packet        -   Redundancy and/or constellation version: Tells the UE, which            hybrid ARQ redundancy version to use (required for rate            matching) and/or which modulation constellation version to            use (required for modulation)        -   UE Identity (UE ID): Tells which UE should transmit data. In            typical implementations this information is used to mask the            CRC of the L1/L2 control signaling in order to prevent other            UEs to read this information.

There are several different flavors how to exactly transmit theinformation pieces mentioned above. Moreover, the L1/L2 controlinformation may also contain additional information or may omit some ofthe information. E.g.:

-   -   HARQ process number may not be needed in case of a synchronous        HARQ protocol    -   A redundancy and/or constellation version may not be needed if        Chase Combining is used (always the same redundancy and/or        constellation version) or if the sequence of redundancy and/or        constellation versions is predefined.    -   Power control information may be additionally included in the        control signaling    -   MIMO related control information, such as e.g., precoding, may        be additionally included in the control signaling.    -   In case of multi-codeword MIMO transmission transport format        and/or HARQ information for multiple code words may be included.

For uplink resource assignments (PUSCH) signaled on PDCCH in LTE, theL1/L2 control information does not contain a HARQ process number, sincea synchronous HARQ protocol is employed for LTE uplink. The HARQ processto be used for an uplink transmission is given by the timing.Furthermore it should be noted that the redundancy version (RV)information is jointly encoded with the transport format information,i.e., the RV info is embedded in the transport format (TF) field. The TFrespectively MCS field has for example a size of 5 bits, whichcorresponds to 32 entries. 3 TF/MCS table entries are reserved forindicating RVs 1, 2 or 3. The remaining MCS table entries are used tosignal the MCS level (TBS) implicitly indicating RV0. The size of theCRC field of the PDCCH is 16 bits. Further detailed information on thecontrol information for uplink resource allocation on PUSCH can be foundin TS36.212 section 5.3.3 and TS36.213 section 8.6.

For downlink assignments (PDSCH) signaled on PDCCH in LTE, theRedundancy Version (RV) is signaled separately in a two-bit field.Furthermore the modulation order information is jointly encoded with thetransport format information. Similar to the uplink case there is 5 bitMCS field signaled on PDCCH. 3 of the entries are reserved to signal anexplicit modulation order, providing no Transport format (Transportblock) info. For the remaining 29 entries modulation order and Transportblock size info are signaled. Further detailed information on thecontrol information for uplink resource allocation on PUSCH can be foundin TS36.212 section 5.3.3 and TS36.213 section 7.1.7, incorporated byreference herein.

E-UTRAN Measurements—Measurement Gaps

The E-UTRAN can configure the UE to report measurement information e.g.,to support the control of the UE mobility. The respective measurementconfiguration elements can be signaled via theRRCConnectionReconfiguration message. For instance, measurement gapsdefine time periods when no uplink or downlink transmissions will bescheduled, so that the UE may perform the measurements. The measurementgaps are common for all gap-assisted measurements. Inter-frequencymeasurements may require the configuration of measurement gaps,depending on the capabilities of the UE (e.g., whether it has a dualreceiver). The UE identifies E-UTRA cells operating on carrierfrequencies other than that of the serving cell. Inter-frequencymeasurements, including cell identification, or performed duringperiodic measurement gaps, unless the UE has more than one receiver. Twopossible gap patterns can be configured by the network, each with alength of 6 ms: in gap pattern #0, the gap occurs every 40 ms, while ingap pattern #1 the gap occurs every 80 ms.

For example, the Reference Signal Received Power (RSRP) is measured bythe UE over the cell-specific reference signals within the measurementbandwidth over a measurement period.

ARQ/Hybrid ARQ (HARQ) Schemes

In LTE there are two levels of re-transmissions for providingreliability, namely, HARQ at the MAC layer and outer ARQ at the RLClayer. The RLC retransmission mechanism is responsible for providingerror-free delivery of data to higher layer. To accomplish this, a(re)transmission protocol operates between the RLC entities in thereceiver and transmitter, e.g., in the acknowledged mode. Although theRLC layer would be capable of handling transmission errors due to noise,unpredictable channel variations, etc., this is in most cases handled bythe HARQ retransmission protocol of the MAC layer. The use of aretransmission mechanism in the RLC layer may therefore seem superfluousat first. However, this is not the case, and the use of both RLC- andMAC-based retransmission mechanisms is in fact well motivated by thedifferences in the feedback signaling. For instance, the RLC-ARQmechanism takes care of the possible NACK to ACK errors that may occurwith the MAC HARQ mechanism.

A common technique for error detection and correction in packettransmission systems over unreliable channels is called hybrid AutomaticRepeat request (HARQ). Hybrid ARQ is a combination of Forward ErrorCorrection (FEC) and ARQ. If a FEC encoded packet is transmitted and thereceiver fails to decode the packet correctly (errors are usuallychecked by a CRC, Cyclic Redundancy Check), the receiver requests aretransmission of the packet

RLC Retransmission Protocol

When the RLC is configured to request retransmission of missing PDUs, itis said to be operating in Acknowledged Mode (AM). This is similar tothe corresponding mechanism used in WCDMA/HSPA.

Overall, there are three operational modes for RLC: Transparent Mode(TM), Unacknowledged Mode (UM), and Acknowledged Mode (AM). Each RLCentity is configured by RRC to operate in one of these modes.

In Transparent Mode no protocol overhead is added to RLC SDUs receivedfrom higher layer. In special cases, transmission with limitedsegmentation/reassembly capability can be accomplished. It has to benegotiated in the radio bearer setup procedure, whethersegmentation/reassembly is used. The transparent mode is e.g., used forvery delay-sensitive services like speech.

In Unacknowledged Mode data delivery is not guaranteed since noretransmission protocol is used. The PDU structure includes sequencenumbers for integrity observations in higher layers. Based on the RLCsequence number, the receiving UM RLC entity can perform reordering ofthe received RLC PDUs. Segmentation and concatenation are provided bymeans of header fields added to the data. The RLC entity inUnacknowledged mode is unidirectional, since there are no associationsdefined between uplink and downlink. If erroneous data is received, thecorresponding PDUs are discarded or marked depending on theconfiguration. In the transmitter, the RLC SDUs which are nottransmitted within a certain time specified by a timer are discarded andremoved from the transmission buffer. The RLC SDUs, received from higherlayer, are segmented/concatenated into RLC PDUs on sender side. Onreceiver side, reassembly is performed correspondingly. Theunacknowledged mode is used for services where error-free delivery is ofless importance compared to short delivery time, for example, forcertain RRC signaling procedures, a cell broadcast service such as MBMSand voice over IP (VoIP).

In Acknowledged Mode the RLC layer supports error correction by means ofan Automatic Repeat Request (ARQ) protocol, and is typically used forIP-based services such as file transfer where error-free data deliveryis of primary interest. RLC retransmissions are for example based on RLCstatus reports, i.e., ACK/NACK, received from the peer RLC receivingentity. The acknowledged mode is designed for a reliable transport ofpacket data through retransmission in the presence of high air-interfacebit error rates. In case of erroneous or lost PDUs, retransmission isconducted by the sender upon reception of an RLC status report from thereceiver.

ARQ is used as a retransmission scheme for retransmission of erroneousor missed PDUs. For instance, by monitoring the incoming sequencenumbers, the receiving RLC entity can identify missing PDUs. Then, anRLC status report can be generated at the receiving RLC side, and fedback to the transmitting RLC entity, requesting retransmission ofmissing or unsuccessfully decoded PDUs. The RLC status report can alsobe polled by the transmitter, i.e., the polling function is used by theRLC transmitter to obtain a status report from RLC receiver so as toinform the RLC transmitter of the reception buffer status. The statusreport provides positive acknowledgements (ACK) or negativeacknowledgment information (NACK) on RLC Data PDUs or portions of them,up to the last RLC Data PDU whose HARQ reordering is complete. The RLCreceiver triggers a status report if a PDU with the polling field set to‘1’ or when an RLC Data PDU is detected as missing. There are certaintriggers defined in subclause 5.2.3 of TS36.322, current version 13.0.0,incorporated herein by reference, which trigger a poll for an RLC statusreport in the RLC transmitter. In the transmitter, transmission is onlyallowed for the PDUs within the transmission window, and thetransmission window is only updated by the RLC status report. Therefore,if the RLC status report is delayed, the transmission window cannot beadvanced and the transmission might get stuck.

The receiver sends the RLC status report to the sender when triggered.

As already mentioned before, in addition to data PDU delivery, controlPDUs can be signaled between the peer entities.

MAC HARQ Protocol

The MAC layer comprises a HARQ entity, which is responsible for thetransmit and receive HARQ operations. The transmit HARQ operationincludes transmission and retransmission of transport blocks, andreception and processing of ACK/NACK signaling. The receive HARQoperation includes reception of transport blocks, combining of thereceived data and generation of ACK/NACK signaling. In order to enablecontinuous transmission while previous transport blocks are beingdecoded, up to eight HARQ processes in parallel are used to supportmultiprocess “Stop-And-Wait” (SAW) HARQ operation. Each HARQ process isresponsible for a separate SAW operation and manages a separate buffer.

The feedback provided by the HARQ protocol is either an Acknowledgment(ACK) or a negative Acknowledgment (NACK). ACK and NACK are generateddepending on whether a transmission could be correctly received or not(e.g., whether decoding was successful). Furthermore, in HARQ operationthe eNB can transmit different coded versions from the originaltransport block in retransmissions so that the UE can employincremental-redundancy-(IR)-combining to get additional coding gain viathe combining gain.

If a FEC-encoded packet is transmitted and the receiver fails to decodethe packet correctly (errors are usually checked by a CRC, CyclicRedundancy Check), the receiver requests a retransmission of the packet.Generally (and throughout this document), the transmission of additionalinformation is called “retransmission (of a packet),” and thisretransmission could but does not necessarily mean a transmission of thesame encoded information; it could also mean the transmission of anyinformation belonging to the packet (e.g., additional redundancyinformation) e.g., by use of different redundancy versions.

In general, HARQ schemes can be categorized as either synchronous orasynchronous, with the retransmissions in each case being eitheradaptive or non-adaptive. Synchronous HARQ means that theretransmissions of transport blocks for each HARQ process occur atpre-defined (periodic) times relative to the initial transmission.Hence, no explicit signaling is required to indicate to the receiver theretransmission schedule, or e.g., the HARQ process number since it canbe inferred from the transmission timing.

In contrast, asynchronous HARQ allows the retransmissions to occur atany time relative to the initial transmission, which offers theflexibility of scheduling retransmissions based on air-interfaceconditions. In this case however, additional explicit signaling isrequired to indicate e.g., the HARQ process to the receiver, in order toallow for a correct combining and protocol operation. In 3GPP LTEsystems, HARQ operations with eight processes are used.

In LTE, asynchronous adaptive HARQ is used for the downlink, andsynchronous HARQ for the uplink. In the uplink, the retransmissions maybe either adaptive or non-adaptive, depending on whether new signalingof the transmission attributes is provided, e.g., in an uplink grant.

In uplink HARQ protocol operation (i.e., for acknowledging uplink datatransmissions) there are two different options on how to schedule aretransmission. Retransmissions are either “scheduled” by a NACK (alsoreferred to as a synchronous non-adaptive retransmission) or areexplicitly scheduled by the network by transmitting a PDCCH (alsoreferred to as synchronous adaptive retransmissions).

In case of a synchronous non-adaptive retransmission, the retransmissionwill use the same parameters as the previous uplink transmission, i.e.,the retransmission will be signaled on the same physical channelresources, respectively uses the same modulation scheme/transportformat. The redundancy version though will change, i.e., cycle throughthe predefined sequence of redundancy versions which is 0, 2, 3, 1.

Since synchronous adaptive retransmissions are explicitly scheduled viathe PDCCH, the eNodeB has the possibility to change certain parametersfor the retransmission. A retransmission could be for example scheduledon a different frequency resource in order to avoid fragmentation in theuplink, or eNodeB could change the modulation scheme or alternativelyindicate to the user equipment what redundancy version to use for theretransmission. It should be noted that the HARQ feedback (ACK/NACK) andPDCCH signaling occurs at the same timing for UL HARQ FDD operation.Therefore, the user equipment only needs to check once whether asynchronous non-adaptive retransmission is triggered (i.e., only a NACKis received) or whether eNodeB requests a synchronous adaptiveretransmission (i.e., PDCCH is also signaled).

The PHICH carries the HARQ feedback, which indicates whether the eNodeBhas correctly received a transmission on the PUSCH. The HARQ indicatoris set to 0 for a positive Acknowledgement (ACK) and 1 for a negativeAcknowledgment (NACK). The PHICH carrying an ACK/NACK message for anuplink data transmission may be transmitted at the same time as thePhysical Downlink Control Channel, PDCCH, for the same user terminal.With such a simultaneous transmission, the user terminal is able todetermine what the PDCCH instructs the terminal to do, i.e., to performa new transmission (new UL grant with toggled NDI) or a retransmission(referred to as adaptive retransmission) (new UL grant without toggledNDI), regardless of the PHICH content. When no PDCCH for the terminal isdetected, the PHICH content dictates the UL HARQ behavior of theterminal, which is summarized in the following.

NACK: the terminal performs a non-adaptive retransmission, i.e., aretransmission on the same uplink resource as previously used by thesame HARQ process

ACK: the terminal does not perform any uplink retransmission and keepsthe data in the HARQ buffer for that HARQ process. A furthertransmission for that HARQ process needs to be explicitly scheduled by asubsequent grant by PDCCH. Until the reception of such grant, theterminal is in a “suspension state.”

This is illustrated in the following Table 11:

HARQ feedback seen PDCCH by the UE seen by the (PHICH) UE UE behaviorACK or NACK New New transmission according to Transmission PDCCH ACK orNACK Retransmission Retransmission according to PDCCH (adaptiveretransmission) ACK None No (re)transmission, keep data in HARQ bufferand a PDDCH is required to resume retransmissions NACK None Non-adaptiveretransmission

The schedule timing of the uplink HARQ protocol in LTE is exemplarilyillustrated in FIG. 3 . The eNB transmits to the UE a first uplink grant301 on PDCCH, in response to which, the UE transmits first data 302 tothe eNB on PUSCH. The timing between the PDCCH uplink grant and thePUSCH transmission is currently fixed to 4 ms. After receiving the firstdata transmission 302 from the UE, the eNB transmits feedbackinformation (ACK/NACK) and possibly an UL grant 303 for the receivedtransmission to the UE (alternatively, when the UL transmission wassuccessful, the eNB could have triggered a new uplink transmission bytransmitting a suitable second uplink grant). The timing between thePUSCH transmission and the corresponding PHICH carrying the feedbackinformation is currently also fixed to 4 ms. Consequently, the RoundTrip Time (RTT) indicating the next (re)transmission opportunity in theuplink HARQ protocol is 8 ms. After these 8 ms, the UE may transmit aretransmission 304 of previous data as instructed by the eNB. For thefurther operation, it is assumed that the retransmission 304 of apreviously transmitted data packet was again not successful such thatthe eNodeB would instruct the UE to perform another retransmission(e.g., transmitting a NACK 305 as a feedback). In response thereto, theUE would thus perform a further retransmission 306.

At the top of FIG. 3 , the subframe numbering is listed as well as anexemplary association of the HARQ processes with the subframes. Asapparent therefrom, each of the 8 available HARQ processes is cyclicallyassociated with a respective subframe. In the exemplary scenario of FIG.3 , it is assumed that the initial transmission 302 and thecorresponding retransmissions thereof 304 and 306 are handled by thesame HARQ process number 5.

Measurement gaps for performing measurements at the UE are of higherpriority than HARQ retransmissions. Thus, whenever an HARQretransmission collides with a measurement gap, the HARQ retransmissiondoes not take place. On the other hand, whenever a HARQ feedbacktransmission over the PHICH collides with a measurement gap, the UEassumes an ACK as the content of the expected HARQ feedback.

There are several fields in the downlink control information to aid theHARQ operation:

-   -   New Data Indicator (NDI): toggled whenever a transmission of a        transport block is scheduled, i.e., also referred to as initial        transmission (“toggled” means that the NDI bit provided in the        associated HARQ information has been changed/toggled compared to        the value in the previous transmission of this HARQ process)    -   Redundancy Version (RV): indicates the RV selected for the        transmission or retransmission    -   MCS: Modulation and Coding scheme

HARQ operation is complex and will/cannot be described in full in thisapplication, nor is it necessary for the full understanding of theinvention. A relevant part of the HARQ operation is defined e.g., in3GPP TS 36.321, version 13.0.0, clause 5.4.2 “HARQ operation,”incorporated by reference herein, and wherein parts thereof will berecited in the following.

5.4.2 HARQ Operation

5.4.2.1 HARQ Entity

There is one HARQ entity at the MAC entity for each Serving Cell withconfigured uplink, which maintains a number of parallel HARQ processesallowing transmissions to take place continuously while waiting for theHARQ feedback on the successful or unsuccessful reception of previoustransmissions.

The number of parallel HARQ processes per HARQ entity is specified in[2], clause 8.

When the physical layer is configured for uplink spatial multiplexing[2], there are two HARQ processes associated with a given TTI. Otherwisethere is one HARQ process associated with a given TTI.

At a given TTI, if an uplink grant is indicated for the TTI, the HARQentity identifies the HARQ process(es) for which a transmission shouldtake place. It also routes the received HARQ feedback (ACK/NACKinformation), MCS and resource, relayed by the physical layer, to theappropriate HARQ process(es).

When TTI bundling is configured, the parameter TTI_BUNDLE_SIZE providesthe number of TTIs of a TTI bundle. TTI bundling operation relies on theHARQ entity for invoking the same HARQ process for each transmissionthat is part of the same bundle. Within a bundle HARQ retransmissionsare non-adaptive and triggered without waiting for feedback fromprevious transmissions according to TTI_BUNDLE_SIZE. The HARQ feedbackof a bundle is only received for the last TTI of the bundle (i.e., theTTI corresponding to TTI_BUNDLE_SIZE), regardless of whether atransmission in that TTI takes place or not (e.g., when a measurementgap occurs). A retransmission of a TTI bundle is also a TTI bundle. TTIbundling is not supported when the MAC entity is configured with one ormore SCells with configured uplink.

TTI bundling is not supported for RN communication with the E-UTRAN incombination with an RN subframe configuration.

For transmission of Msg3 during Random Access (see subclause 5.1.5) TTIbundling does not apply.

For each TTI, the HARQ entity shall:

-   -   identify the HARQ process(es) associated with this TTI, and for        each identified HARQ process:        -   if an uplink grant has been indicated for this process and            this TTI:        -   if the received grant was not addressed to a Temporary            C-RNTI on PDCCH and if the NDI provided in the associated            HARQ information has been toggled compared to the value in            the previous transmission of this HARQ process; or        -   if the uplink grant was received on PDCCH for the C-RNTI and            the HARQ buffer of the identified process is empty; or        -   if the uplink grant was received in a Random Access            Response:            -   if there is a MAC PDU in the Msg3 buffer and the uplink                grant was received in a Random Access Response:                -   obtain the MAC PDU to transmit from the Msg3 buffer.            -   else:                -   obtain the MAC PDU to transmit from the                    “Multiplexing and assembly” entity;            -   deliver the MAC PDU and the uplink grant and the HARQ                information to the identified HARQ process;            -   instruct the identified HARQ process to trigger a new                transmission.        -   else:            -   deliver the uplink grant and the HARQ information                (redundancy version) to the identified HARQ process;            -   instruct the identified HARQ process to generate an                adaptive retransmission.        -   else, if the HARQ buffer of this HARQ process is not empty:            -   instruct the identified HARQ process to generate a                non-adaptive retransmission.

When determining if NDI has been toggled compared to the value in theprevious transmission the MAC entity shall ignore NDI received in alluplink grants on PDCCH for its Temporary C-RNTI.

Uplink HARQ Protocol for NB-IoT/eMTC

For NB-IoT as well as eMTC (Rel-13), an asynchronous UL HARQ protocolhas been introduced (and is being discussed for the ongoing Rel-14 workitem for uplink on unlicensed carriers). Different to the synchronousUplink HARQ protocol used for legacy LTE, retransmissions for NB-IoT oreMTC UEs are adaptive and asynchronous. More in particular theretransmissions don't need to occur at a fixed timing relative to theprevious HARQ transmission for the same process, which offers theflexibility of scheduling retransmissions explicitly. Furthermore therewill be no explicit HARQ feedback channel (PHICH), i.e.,retransmissions/initial transmissions are indicated by PDCCH (NDIdistinguished between initial and retransmission). Essentially theuplink HARQ protocol behavior for NB-IoT or eMTC UEs will be verysimilar to the asynchronous HARQ protocol used for the downlink sinceRel-8.

It should be noted that for NB IoT there will be only one UL HARQprocess.

For more information on the asynchronous uplink HARQ protocol introducedfor NB-IoT/eMTC UEs, it is referred to section 5.4.2 of 3GPP TS 36.321V13.1.0 (2016 -03), incorporated by reference herein.

Short Latency Study Item

Packet data latency is one of the performance metrics that vendors,operators and also end-users (via speed test applications) regularlymeasure. Latency measurements are done in all phases of a radio accessnetwork system lifetime, when verifying a new software release or systemcomponent, when deploying a system and when the system is in commercialoperation.

Better latency than previous generations of 3GPP RATs was oneperformance metric that guided the design of LTE. LTE is also nowrecognized by the end-users to be a system that provides faster accessto internet and lower data latencies than previous generations of mobileradio technologies.

In the 3GPP community, much effort has been put into increasing datarates from the first release of LTE (release 8) until the most recentone (release 12). Features like Carrier Aggregation (CA), 8×8 MIMO, 256QAM have raised the technology potential of the L1 data rate from 300Mbps to 4 Gbps. In Rel-13, 3GPP aims to introduce even higher bit ratesby introducing up to 32 component carriers in CA.

However, with respect to further improvements specifically targeting thedelays in the system little has been done. Packet data latency isimportant not only for the perceived responsiveness of the system; it isalso a parameter that indirectly influences the throughput. HTTP/TCP isthe dominating application and transport layer protocol suite used onthe internet today. According to HTTP Archive(http://httparchive.org/trends.php) the typical size of HTTP-basedtransactions over the internet are in the range from a few 10's ofKbytes up to 1 Mbyte. In this size range, the TCP slow start period is asignificant part of the total transport period of the packet stream.During TCP slow start the performance is latency limited. Hence,improved latency can rather easily be shown to improve the averagethroughput, for this type of TCP-based data transactions. In addition,to achieve really high bit rates (in the range of Gbps with Rel-13 CA),UE buffers need to be dimensioned correspondingly. The longer the RTTis, the bigger the buffers need to be. The only way to reduce bufferingrequirements in the UE and eNB side is to reduce latency.

Radio resource efficiency could also be positively impacted by latencyreductions. Lower packet data latency could increase the number oftransmission attempts possible within a certain delay bound; hencehigher BLER targets could be used for the data transmissions, freeing upradio resources but still keeping the same level of robustness for usersin poor radio conditions. The increased number of possible transmissionswithin a certain delay bound, could also translate into more robusttransmissions of real-time data streams (e.g., VoLTE), if keeping thesame BLER target. This would improve the VoLTE voice system capacity.

There are more over a number of existing applications that would bepositively impacted by reduced latency in terms of increased perceivedquality of experience: examples are gaming, real-time applications likeVoLTE/OTT VoIP and video telephony/conferencing.

Going into the future, there will be a number of new applications thatwill be more and more delay critical. Examples include remotecontrol/driving of vehicles, augmented reality applications in e.g.,smart glasses, or specific machine communications requiring low latencyas well as critical communications.

Various pre-scheduling strategies can be used to lower the latency tosome extent, but similarly to shorter Scheduling Request (SR) intervalintroduced in Rel-9, they do not necessarily address all efficiencyaspects.

It should also be noted that reduced latency of user plane data may alsoindirectly give shorter call set-up/bearer set-up times, due to fastertransport of control signaling.

To ensure LTE evolution and competitiveness it appears thereforenecessary to study and improve the packet data latencies.

The objective of this study item is to study enhancements to the E-UTRANradio system in order to:

-   -   Significantly reduce the packet data latency over the LTE Uu air        interface for an active UE, and    -   Significantly reduce the packet data transport round trip        latency for UEs that have been inactive for a longer period (in        connected state).

The study area includes resource efficiency, including air interfacecapacity, battery lifetime, control channel resources, specificationimpact and technical feasibility. Both FDD and TDD duplex modes areconsidered.

As first aspect, potential gains like reduced response time and improvedTCP throughput due to latency improvements on typical applications anduse cases are identified and documented. In conclusion, this aspect ofthe study is supposed to show what latency reductions would bedesirable.

As second aspect, the following areas should be studied and documented:

-   -   Fast uplink access solutions:        -   for active UEs and UEs that have been inactive a longer            time, but are kept in RRC Connected, focus should be on            reducing user plane latency for the scheduled UL            transmission and getting a more resource efficient solution            with protocol and signaling enhancements, compared to the            pre-scheduling solutions allowed by the standard today, both            with and without preserving the current TTI length and            processing times;    -   TTI shortening and reduced processing times:        -   Assess specification impact and study feasibility and            performance of TTI lengths between 0.5 ms and one OFDM            symbol, taking into account impact on reference signals and            physical layer control signaling;        -   backwards compatibility shall be preserved (thus allowing            normal operation of pre-Rel 13 UEs on the same carrier).

Processing Chain Functions for Uplink

The processing chain as illustrated in FIG. 4 is taken from section5.2.2 of 3GPP TS 36.212 V13.1.0 (2016-03), incorporated by referenceherein.

FIG. 4 shows a block diagram including coding chain functionalitieswithin the physical layer for a single codeword/transport block. Theinput consists of the transport block handed down by the MAC layer. Forretransmissions of a transport block, the redundancy version (RV) is aninput parameter within the “Rate matching block.” Consequently, if aretransmission uses a different RV, at least the blocks “Rate matching,”“Code block concatenation,” “Data and Control multiplexing,” and“Channel Interleaver” need to be processed.

The output of the block “Channel Interleaver” serves as a “codeword”input to the physical channel processing steps shown in FIG. 5 , whichis taken from section 5.3 of 3GPP TS 36.211 V13.1.0 (2016-03),incorporated by reference herein.

FIG. 5 shows a block diagram including physical channel processingfunctionalities within the physical layer. The input consists of thecodeword(s) obtained as the result of the coding chain depicted in FIG.5.2.2-1 of 3GPP TS 36.212. It should be noted that for normal (non-MTCor NB-IoT) processing, the “Scrambling” block has among its inputparameters the transmission subframe index within a radio frame.Therefore the output of the “Scrambling” block is different fordifferent subframe indices, even if the codeword(s) input should beidentical. For retransmissions of a transport block, the redundancyversion (RV) is an input parameter within the “Rate matching block.”Consequently, if a retransmission uses a different RV, at least theblocks “Rate matching,” “Code block concatenation,” “Data and Controlmultiplexing,” and “Channel Interleaver” need to be processed.

BRIEF SUMMARY

Non-limiting and exemplary embodiments provide an improved transmissionprotocol operation for uplink data packet transmissions for a userequipment.

The independent claims provide non-limiting and exemplary embodiments.Advantageous embodiments are subject to the dependent claims.

According to several aspects described herein, the transmission protocoloperation shall be improved.

According to one general aspect, a user equipment is described thatoperates a transmission protocol for uplink data packet transmission ina communication system, wherein the user equipment comprises a receiverthat receives a Fast Retransmission Indicator. Thereby, the FastRetransmission Indicator indicates whether or not a base stationrequests a retransmission of a previously transmitted data packet. Theuser equipment comprises a transmitter that retransmits the data packetusing the same redundancy version as already used for the previoustransmission of the data packet.

According to another general aspect, a base station is described thatoperates a transmission protocol for uplink data packet transmission ina communication system, wherein the base station comprises a transmitterthat transmits a Fast Retransmission Indicator. Thereby, the FastRetransmission Indicator indicates to the user equipment whether or notthe base station requests a retransmission of a previously transmitteddata packet. The base station comprises a receiver that receives, fromthe user equipment, the retransmitted data packet with the sameredundancy version as already used, by the user equipment, for theprevious transmission of the data packet.

Correspondingly, in another general aspect, the techniques disclosedhere feature a method for operating a transmission protocol in a userequipment for uplink data packet transmission in a communication system.The method comprises receiving a Fast Retransmission Indicator, referredto as FRI, wherein the FRI indicates whether or not a base stationrequests a retransmission of a previously transmitted data packet. Themethod further comprises retransmitting the data packet using the sameredundancy version as already used for the previous transmission of thedata packet.

Correspondingly, in another general aspect, the techniques disclosedhere feature a method for operating a transmission protocol in a basestation for uplink data packet transmission in a communication system.The method comprises transmitting a Fast Retransmission Indicator,referred to as FRI, wherein the FRI indicates to a user equipmentwhether or not a retransmission of a previously transmitted data packetis requested. The method further comprises receiving, from the userequipment, the retransmitted data packet with the same redundancyversion as already used, by the user equipment, for the previoustransmission of the data packet.

Additional benefits and advantages of the disclosed embodiments will beapparent from the specification and figures. The benefits and/oradvantages may be individually provided by the various embodiments andfeatures of the specification and drawings disclosure, and need not allbe provided in order to obtain one or more of the same.

These general and specific aspects may be implemented using a system, amethod, and a computer program, and any combination of systems, methods,and computer programs.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the following exemplary embodiments are described in more detail withreference to the attached figures and drawings.

FIG. 1 shows an exemplary architecture of a 3GPP LTE system,

FIG. 2 shows an exemplary downlink resource grid of a downlink slot of asubframe as defined for 3GPP LTE (Release 8/9),

FIG. 3 exemplary illustrates the transmission protocol operation betweenthe UE and the eNodeB for an uplink transmission and itsretransmissions,

FIG. 4 schematically illustrates a block diagram including coding chainfunctionalities within the physical layer for a singlecodeword/transport block,

FIG. 5 schematically illustrates a block diagram including physicalchannel processing functionalities within the physical layer,

FIG. 6 illustrates a timing diagram of the transmission requests and thecorresponding transmissions, according to the embodiment, and

FIG. 7 illustrates a timing diagram of the transmission requests and thecorresponding transmissions in case of a conflict between simultaneouslyrequested retransmissions, according to the embodiment.

DETAILED DESCRIPTION

As can be seen from FIG. 3 and the description thereof in the backgroundsection, there is currently a delay of 4 ms between a PDCCH/PHICH and acorresponding PUSCH uplink transmission. This delay is mainly caused dueto the processing that needs to be done at the UE side, including thedetection of PDCCH/PHICH as well as the coding chain and physicalchannel processing steps outlined above. Even though this latency of 4ms could be reduced by shortening the TTI as is being discussed withinthe scope of the above-described Short Latency study item, the mainsavings in time would be due to the smaller transport block sizes and apotentially improved hardware/software design that allows fasterprocessing. Nevertheless, the savings are still bounded by the need forprocessing all the functional blocks in the transmission chain asoutlined above, even for a retransmission, especially when a differentRV is used for a retransmission compared to the previous transmission ofthe same transport block (data packet).

Another delay that is currently 4 ms long is the gap between a PUSCHtransmission and the next potential trigger by PDCCH/PHICH for the sameHARQ process. This gap is caused by the need of the eNB to process thePUSCH and attempt the decoding of same, and in case of an unsuccessfuldecoding attempt, to determine again the proper scheduling and linkadaptation procedures to determine an appropriate set of physical layertransmission parameters (including the MCS, number and position of RBs,RV, transmit power) for the retransmissions, which needs to take otherusers' needs for uplink transmission into account as well. Finally, oncethese parameters are determined, they need to be conveyed to the UE by aDCI on (E)PDCCH (for an adaptive retransmission) and/or by an HI on aPHICH (for a non-adaptive retransmission).

Even though a PHICH could be seen as a compact method to trigger anon-adaptive retransmission, especially due to the different RV versionand the subframe-dependent scrambling, the UE would still need toexecute a substantial number of steps before being able to transmit.

The object of the invention is to reduce the delay between thetransmission on PUSCH from the UE and a corresponding retransmissionindication by the eNodeB. A further object is to also to reduce thedelay between an indication for a retransmission by the eNodeB and thecorresponding retransmission on PUSCH from the UE.

The following exemplary embodiment is conceived by the inventors tomitigate one or more of the problems explained above.

Particular implementations of the several variants of the embodiment areto be implemented in the wide specification as given by the 3GPPstandards and explained partly in the background section, with theparticular key features being added as explained in the followingpertaining to the described embodiment. It should be noted that theembodiment may be advantageously used for example in a mobilecommunication system, such as 3GPP LTE-A (Release 10/11/12/13)communication systems as described in the Technical Background sectionabove, but the embodiment is not limited to its use in this particularexemplary communication networks.

The explanations should not be understood as limiting the scope of thedisclosure, but as a mere example of the embodiment to better understandthe present disclosure. A skilled person should be aware that thegeneral principles of the present disclosure as laid out in the claimscan be applied to different scenarios and in ways that are notexplicitly described herein. For illustration purposes, severalassumptions are made which however shall not restrict the scope of thefollowing embodiment.

In the following, an embodiment for solving the above-mentionedproblem(s) will be described in detail. Different implementations andvariants of the embodiment will be explained as well.

The embodiment provides a user equipment (UE) operating a transmissionprotocol for uplink data packet transmission in a communication system.According to the transmission protocol, a Fast Retransmission Indicator(FM) is used for triggering a faster retransmission at the UE withreduced timing in case of an unsuccessful PUSCH decoding attempt at theeNodeB. If employing this FM, it is possible to transmit aretransmission request earlier by the eNodeB than it is possible withthe use of a DCI/HI.

In order for the UE to retransmit a data packet quicker than it would bepossible in response to a DCI, the UE may use, according to one variantof the embodiment, for its retransmission of the data packet not onlythe same radio resources as if a non-adaptive retransmission istriggered by HI, but also uses other identical parameters as they wereapplicable for the latest transmitted data packet, which was triggeredby a DCI or HI.

Likewise, the embodiment provides a base station operating atransmission protocol for uplink data packet transmission where the FRIis transmitted to the UEs so as to indicate whether or not aretransmission of a previously transmitted data packet is requested. Inreaction to such request, the base station receives from the UE theretransmitted data packet with the same redundancy version as alreadyused for the previous transmission of the data packet.

As a general consideration, if the eNodeB intends to trigger a fastretransmission of a data packet, e.g., due to a time-criticalQuality-of-Service requirement, it is more important to have aretransmission as fast as possible at the possible expense of anon-optimum use of the radio channel capacity. As a key aspect forachieving such a fast retransmission of the data packet, the eNodeB doesnot need to make a full link adaptation assessment since all parametersare already decided for the previous transmission of the data packet.

In the background section it has already been explained that, even ifusing a HI for retransmission, the redundancy version will change forthe retransmitted data block. In this case, the redundancy version iscycled through the predefined sequence of redundancy versions, which is0, 2, 3, 1, for instance. The specific selected redundancy version forthe retransmission is an input value for the “rate matching” block, asillustrated in FIG. 4 . Hence, for each retransmitted data block thatuses a different redundancy version (RV), at least the blocks “ratematching,” “Code block concatenation,” “Data and Control multiplexing,”and “Channel Interleaver” have to be processed again. Also, the outputof the “Channel Interleaver” block then is input to the entire physicalchannel processing, which is illustrated in FIG. 5 .

In order to achieve a significant reduction of the time needed fortransmitting a retransmission of the data packet, in one implementationof the embodiment the UE uses for its retransmission of the data packetthe same redundancy version as already used for the previoustransmission of the data packet. Due to the UE using for itsretransmission of the data packet a subset of identical transmissionparameters as for the previous DCI-triggered transmission, namely thesame redundancy version as for the previously transmitted data packet,all processing steps involved with the change of the redundancy versionof the data packet can be skipped.

That is, even in case of only using the same RV as for the previous DCI(or HI) triggered transmission of a data packet, no new “rate matching”and subsequent blocks (as shown in FIG. 4 ) up to the beginning of thescrambling (as shown in FIG. 5 ) need to be processed. In other words,for a fast retransmission it is sufficient, if the UE buffers thecodewords as they are transmitted in the most recent transmission, anddoes feed those buffered codewords into the physical channel processingprocedure, as shown in FIG. 5 .

In FIG. 6 , a timing diagram of the transmission requests and thecorresponding transmissions is shown. As can be seen from this figure,the time period between the transmission of a DCI by the eNodeB as wellas the corresponding transmission of the data packet by the UE isindicated as time period t0, wherein the time period t0 may be named as“third timing.” For an uplink HARQ protocol as employed since LTERelease 8, time period t0 corresponds to the time period of 4 ms asshown in FIG. 3 , where the conventional case is illustrated thatrelates to triggering an uplink data transmission by a DCI. As can beobtained from FIG. 6 , and in contrast to FIG. 3 , the time period t1(as also shown in FIG. 6 ) between the transmission of a data packet bythe UE (PUSCH) and the transmission of the FRI by the eNodeB may beequal to or shorter than t0, whereas in a preferred variant of theembodiment, t1, however, is smaller than time period t0. While timeperiod t0 may become smaller than 4 ms in the further development in thefuture, not limiting the scope of the invention the description of theembodiments assumes that time period t0 is 4 ms, unless otherwisestated.

Thereby, as a further variant of the embodiment, the time period t1,which may be named as “first timing,” is a fixed time period or a timeperiod that is semi-statically configurable by the base station, andwherein, preferably, time period t1 may be smaller than 4 ms.

It is to be noted that an FRI generally can indicate at least twostates. According to “State 1,” the FRI is a “positive FRI” and triggersa fast retransmission, whereas in this case, the FRI could be seen as anegative acknowledgment of a received data packet. According to “State2,” the FRI is a “negative FRI” and does not trigger a fasterretransmission, since in this case, the FRI could be seen as a positiveacknowledgment of a received data packet. A functionally equivalentinterpretation of states is therefore that a “positive FRI” isequivalent to an FRI carrying a “negative acknowledgement (NACK),” and a“negative FRI” is equivalent to an FRI carrying an “acknowledgement(ACK).” For simplicity and without restricting the scope of theembodiment, the description hereafter uses only the terminology“positive FRI” and “negative FRI.”

As further derivable from FIG. 6 , the time period t2, which is definedas the time between a positive FRI sent by the eNodeB and itscorresponding PUSCH transmission sent by the UE, must be smaller thantime period t0, which is the time period between a DCI (or HI) and itscorresponding PUSCH transmission. The shorter time period t2 compared tothe time period t0 is the result of saving calculation time at the UEdue to using, for a retransmission of a data packet, a subset ofidentical transmission parameters as for the previous DCI-/HI-triggeredtransmission as described above. The use of the identical redundancyversion is illustrated in FIG. 6 . For example, for both, the PUSCHtransmission that is initiated by the DCI as well as the PUSCHtransmission that is initiated by the FRI are carried out by usingredundancy version RV #0. In other words, RV #0 was determined accordingto the DCI initiated PUSCH transmission and reused by the FRI initiatedPUSCH transmission.

Thereby, as a further variant of the embodiment, the time period t2,which may be named as “second timing,” is a fixed time period or a timeperiod that is semi-statically configurable by the base station orvariable based on a respective information comprised in thetransmitted/received FRI. Preferably, time period t2 may be smaller than4 ms.

According to a further implementation of the embodiment, the positiveFRI indicates that the retransmission is to be performed with additionaltransmission parameters identical to same used for the previoustransmission of the data packet, whereas these additional identicaltransmission parameters are then used for retransmitting the data packetby the UE and for receiving the retransmitted data packet at the basestation.

According to a further implementation of the embodiment, the additionalidentical transmission parameter to be used for retransmitting the datapacket is at least the scrambling code of the previously transmitteddata packet. As an advantage of having further identical transmissionparameters such as the same scrambling code is that in addition to theabove mentioned skipping of the blocks “rate matching” to “ChannelInterleaver” as shown in FIG. 4 , also the “scrambling” block as shownin FIG. 5 does not need to be processed for the retransmitted datapacket.

In further variants of the embodiment, additional identical transmissionparameters may be re-used from a previous DCI initiated PUSCHtransmission, up to the point where the precoded information isavailable, i.e., after the block “Precoding” in FIG. 5 . For example,further additional identical transmission parameters may be re-using themodulation scheme and the layer mapping from a previous DCI initiatedPUSCH transmission, so that the same transmission scheme is used for theretransmission as for the previous transmission, i.e., the same numberof transmission layers and the same antenna ports are used. Using thesame precoding vector(s) as in the previous transmission is mostreasonable in case the FRI does not indicate a different precoder to beused.

However, if re-using further identical transmission parameters from aprevious DCI initiated PUSCH transmission beyond the block “Precoding”as shown in FIG. 5 , then only a part of the resources are utilized forthe retransmission. For example, the “Resource Element Mapper” blockwould only map data to a part of the resources that had been used forthe previous transmission, e.g., a fraction of the resource blocks suchas, for example, 50% of the resource blocks. Equivalently, for a fastretransmission, only a fraction of the output of the “Resource ElementMapper” block is used as input to the “SC-FDMA signal generation” block.Therefore, it would be sufficient if the UE buffers the output of the“Resource Element Mapper” block(s) of the previous transmission, andupon being triggered for a partial retransmission, reads only thecorresponding parts from the buffer and applies these as the input tothe SC-FDMA signal generation. Preferably, the fraction used for a fastretransmission consists of a non-negative integer multiple of a basictime or frequency resource unit, such as a “resource block” or a“resource block group” as defined in TS 36.213. This has the advantagethat unused resources can be optimally assigned to other UEs, i.e.,without wasting resources caused by a fractional resource block orresource block group. In addition, the fraction should result in abandwidth of the PUSCH in terms of resource blocks M_(RB) ^(PUSCH),where M_(RB) ^(PUSCH)=2^(α) ² ·3^(α) ³ ·5^(α) ⁵ and where α₂, α₃, α₅ isa set of non-negative integers. Therefore, if the indicated fractionwould result in a non-integer number of resource blocks, or resourceblock groups, or if the resulting bandwidth M_(RB) ^(PUSCH) would notfulfill the condition M_(RB) ^(PUSCH)=2^(α) ² ·3^(α) ³ ·5^(α) ⁵ , the UEshould preferably round up to the smallest integer number of resourceblocks, or resource block groups than the indicated fraction, or to thesmallest integer value M_(RB) ^(PUSCH) greater than the indicatedfraction that fulfils M_(RB) ^(PUSCH)=2^(α) ² ·3^(α) ³ ·5^(α) ⁵ ,respectively.

In a further variant of the embodiment, as an additional identicaltransmission parameter, the same “cyclic shift parameter” may be used asfor the generation of the reference signals for the retransmission ofthe data packet. In this regard, reference is made to section 5.5.2 of3GPP technical standard 36.211. Using the identical “cyclic shiftparameter” for the generated reference signals results in a furtherreduction of the overall processing time for the retransmission. Inanother variant, the FRI transmitted by the eNodeB may further compriseinformation with regards to the “cyclic shift parameter,” which is to beused by the UEs for the generation of the reference signals for theretransmission of the data packet.

It may happen that the most recent transmission of a data block does notonly consist of UL-SCH data, but includes uplink control information(UCI) such as ACK/NACK, CSI. As can be seen in FIG. 4 , such informationis added to the data in the block “Data and control multiplexing.”Generally, such information is preferably also added in a retransmissiontriggered by FRI in the same way as in the most recent transmission ofthe data block. However, transmitting the identical ACK/NACK or CSIinformation is not necessarily reasonable, as the content would beoutdated due to the delay between the previous transmission and thetriggered retransmission. Therefore, an alternative embodiment does notinclude the UCI in the retransmission, but reserves those resources asif the information was present. As a consequence, the order of datablock bits can be unchanged, so that no further bit reordering procedureis necessary for a retransmission.

Likewise, a part of the resources of an uplink subframe may containsounding reference symbols (SRS), preferably at the end of a subframe.In such a case, a fast retransmission may then also contain the SRS asin the previous transmission, or the resources are reserved (e.g.,muted). As a consequence, the mapping of the PUSCH to the resourceelements can remain unchanged, so that no further RE reorderingprocedure is necessary for a retransmission.

With reference to FIGS. 6 and 7 , it is to be noted that the eNodeB mayflexibly determine in case a data packet has not successfully beenreceived, whether a retransmission for the data packet is requested fromthe UE by using the FRI, or by using a DCI, or by using a HI and thus totransmit either the FRI, the DCI, or the HI to the UE. Likewise, the UEmay also flexibly react on the reception of either an FRI, a DCI, or anHI and perform a corresponding transmission/retransmission of the datapacket based on the received FRI, DCI, or the HI, as described above.

According to a further implementation of the embodiment, the FRIindicates that a retransmission of a part of the previously transmitteddata packet is to be performed, optionally wherein a part is 50% or 25%of the previously transmitted data packet. In such a case, the UEretransmits the indicated part of the previously transmitted datapacket. The UE may adapt the transmit power for the retransmission ofthe part of the previously transmitted data packet so that the totaltransmit power for the retransmission equals the total transmit power ofthe previously transmitted data packet, optionally wherein using 50% ofthe data packet results in a transmission power increase of the part ofthe previously transmitted data packet by a factor 2.

If for a retransmission only a fraction of the frequency resources ofthe previous transmission are utilized, the total power that the UEwould transmit for the partial retransmission would also be a fraction.However, in order to improve the quality of the partial retransmissiondata, its power can be boosted reciprocally to the fraction of thefrequency resources. For example, if a partial retransmission utilizesonly 50% of the frequency resources, then each RE of the partialretransmission can be boosted by a factor of 2, so that the totaltransmit power when regarding all transmitted REs for the partialretransmission and the full retransmission is equal. Such a partialretransmission is particularly attractive, if there is no need for afull retransmission to arrive at a successful decoding of the transportblock, or if the eNodeB intends to use only parts of the frequencyresources for the retransmission so that the remaining parts can bescheduled to another UE.

The amount of frequency resources to be utilized for a partialretransmission can be determined according to:

1. A semi-static configuration: Whenever a positive FRI triggers a fastretransmission, the UE looks up the configured value and applies itaccordingly.

2. An indication within the FRI: The FRI can carry an indicator todetermine the amount of partial resources. For example, a first FRIvalue triggers a partial retransmission of 50%, a second FRI valuetriggers a partial retransmission of 25%, a third value triggers a fullretransmission (i.e., 100%), while a fourth FRI value triggers no fastretransmission. Therefore, there would be three positive and onenegative FRI values in this example.

Combinations of these are possible, e.g., the eNodeB configures threedifferent partial retransmission values (possibly including 100%), andthen each of the positive FRI values points to the correspondingsemi-static partial retransmission value, respectively (with one FRIvalue indicating no fast retransmission, i.e., one negative FRI value).

In a further implementation of the embodiment, the user equipment maycomprise multiple transmitting antennas for transmission of datapackets. In this case, the received FRI triggers a retransmission of thedata packets so that the UE retransmits the data packets to the eNode Busing the multiple transmitting antennas. That is, in case that atransmission contains two transport blocks (codewords) as in SU-MIMO, apositive FRI would preferably indicate a retransmission of bothtransport blocks to re-use the transmission buffer as much as possiblewithout excessive PHY re-processing, as can be appreciated in relationto FIG. 5 . According to this case and referring to FIG. 5 , re-usingthe transmission buffer in case of retransmitting both transport blocksinvolves that there is no need for processing the illustrated blocks ofFIG. 5 at all. That is, the retransmission of the two transport blockstakes place right after the respective “SC-FDMA signal generation” blockand can be directly transmitted to the eNodeB without furtherprocessing.

At the eNodeB side, which may also use multiple antennas, upontransmitting the FRI that triggers the retransmission of the transportblocks, the retransmitted transport blocks are received at the eNodeBusing the multiple receiving antennas.

However, triggering a retransmission of both transport blocks by (onesingle) FRI comes at the expense of radio resource efficiency andsignal-to-noise ratio. Therefore an alternative implementation of theembodiment would trigger a retransmission of one transport block per FRIso that the retransmission of the one transport block to the eNodeB aswell as the reception of the one transport block at the eNodeB iscarried out by using the multiple transmitting antennas. It is to benoted that in this case, more processing is required at the UE until theSC-FDMA signals are available for transmission. That is, with referenceto FIG. 5 , if the FRI triggers a retransmission of only one transportblock, this involves the processing of the “Layer mapping” block up tothe “SC-FDMA signal generation” blocks.

The above description relates to the behavior for retransmission,according to which it is assumed that data for the same transport blocksis used in transmissions and retransmissions, i.e., implying that aretransmission applies to the same HARQ process. However, there may alsobe multiple HARQ processes that can be scheduled concurrently-followinga synchronous or an asynchronous protocol.

In both cases, a fast retransmission would occur in a TTI at time“#t_pusch,” as illustrated in FIG. 7 . A PUSCH transmission at time“#t_pusch” could therefore be triggered by a positive FRI at time“#t_pusch-t2,” or by a DCI (or HI) at time “#t_pusch-t0,” and generallyfor different HARQ processes. Therefore, in FIG. 7 , different HARQprocesses P0 and P1 are illustrated. In the exemplary case as shown inFIG. 7 , HARQ process P0 relates to the FRI initiated retransmission attime “#t_pusch,” whereas HARQ process P1 relates to the DCI initiatedretransmission at the time “#t_pusch-t0.”

As further shown in FIG. 7 , the retransmissions for both HARQ processesP0 and P1 would result in a retransmission at time “#t_pusch.” However,in order to avoid a transmission collision, the UE needs to decide whatit should do at time “#t_pusch.” The first option would be to carry onwith a retransmission for HARQ process P0, i.e., follow the FRI triggerreceived at time “#t_pusch-t2.” The second option would be to carry onwith a retransmission for HARQ process P1, i.e., follow the DCI (or HI)received at time “#t_pusch-t0.”

In this regard, a preferred implementation of the embodiment relates tothe specific behavior of the UE, such that it follows the request by theFRI (that is, the afore-mentioned first option) and ignores the requestby the DCI or HI, in case of receiving a request for performing theretransmission of the data packet by the FRI as well as a request forperforming, at the same time, transmission of another data packet by theDCI or HI.

As shown in the background section, when there is a conflict between HIand DCI, the UE follows the DCI and ignores the HI. However, contrarythereto, in the case as provided by the alternative implementation ofthe embodiment, the fast retransmission should be followed and the DCI(or HI) should be ignored. This is because the positive FRI has beentransmitted at a later point in time than the DCI corresponding to thesame subframe. Consequently, it should be assumed that the eNodeB wouldonly transmit a positive FRI in case it intends the UE to follow thepositive FRI—and not the DCI. Otherwise it would not have triggered aretransmission by a positive FRI for that subframe.

As already described in connection with FIG. 6 , also for the case thatthe UE follows the request by the FRI so as to avoid a transmissioncollision, as illustrated in FIG. 7 , the use of the identicalredundancy version for both, the PUSCH transmission that is initiated bythe DCI as well as the PUSCH transmission that is initiated by the FRIare carried out by using redundancy version RV #0. In other words, RV #0was determined according to the DCI initiated PUSCH transmission andre-used by the FRI initiated PUSCH transmission.

Moreover, in a further variant of the embodiment, the FRI furthercomprises an HARQ process number indicator so as to indicate theparticular HARQ process that was used by the transmitter for theprevious transmission of the data packet.

In the table below, the UE behavior is shown for several cases withrespect to the content of received FRI and DCI/HI.

Content Content of the of the FRI DCI (or HI) received received by theby the UE UE UE behavior Negative Request for New transmission accordingto DCI FRI New (or HI) Transmission Negative Request for Retransmissionaccording to DCI FRI Retransmission (adaptive retransmission) oraccording to HI (non-adaptive retransmission) Negative None No(re)transmission FRI Positive None Fast retransmission FRI PositiveRequest for Fast retransmission, wherein data for FRI New the HARQprocess is kept Transmission corresponding to the DCI/HI in the or forbuffer. A DCI is required to resume Retransmission retransmissions forthat HARQ process.

In the table below, an alternative UE behavior is shown for severalcases with respect to the content of received FRI and DCI/HI.

HARQ Content of feedback the FRI seen by received by the UE DCI seen bythe UE (HI) the UE UE behavior Negative ACK or Request for Newtransmission FRI NACK New according to DCI Transmission Negative ACK orRequest for Retransmission according to FRI NACK Retransmission DCI(adaptive retransmission) Negative ACK None No (re)transmission FRINegative NACK None Non-adaptive FRI retransmission Positive ACK NoneFast retransmission FRI Positive NACK None Fast retransmission, whereinFRI data is kept for the HARQ process corresponding to the HI in thebuffer. A DCI is required to resume retransmissions for that HARQprocess. Positive ACK or Request for Fast retransmission, wherein FRINACK New data is kept for the HARQ Transmission or process correspondingto the Retransmission DCI/HI in the buffer. A DCI is required to resumeretransmissions for that HARQ process.

With reference to the description provided above, the FRI may, accordingto one variant of the embodiment, indicate at least one of the followingelements:

-   -   Whether or not a fast retransmission is triggered (positive FRI        or negative FRI, or alternatively NACK or ACK);    -   In case of a triggered fast retransmission: The HARQ process        number indicator for the triggered retransmission;    -   In case of a triggered fast retransmission: A fractional        retransmission parameter indicating the requested part of the        data block to be retransmitted;    -   In case of a triggered fast retransmission: An indication about        the time period t2 until the UE should transmit accordingly.

According to another implementation of the embodiment, the UE receivesthe FRI in radio resources used for receiving the HI, or receives theFRI as a DCI (for example, in DCI format 7), or receives the FRI inpreconfigured radio resources of a common search space, or receives theFRI in preconfigured radio resources of a user-equipment-specific searchspace.

Generally, the FRI can be transmitted in one of the following ways:

-   -   In the same RE(s) where a UE would expect to find a PHICH (but        in a different subframe in case that time period t1 is smaller        than the time between a PUSCH transmission and the subframe        carrying the corresponding HI), i.e., in RE(s) belonging to REGs        within the control channel region of a subframe/TTI, or    -   In RE(s) belonging to a common search space for DCI, i.e., in        REs where all UEs detect FRI, or    -   In a DCI, where preferably FRI for multiple UEs and/or subframes        are multiplexed. For example, the DCI could contain four FRI,        where the first FRI is applicable to UE1, the second FRI is        applicable to UE2, and so on. Especially for TDD systems,        several FRI could be multiplexed or bundled for one UE into a        DCI, so that e.g., the first four FRI are applicable to four        PUSCH transmissions of UE1, the next three FRI are applicable to        three PUSCH transmissions of UE2, and so on. In case that FRI        for multiple UEs are multiplexed, preferably the DCI is        transmitted in the common search space. In case that FRI for        only one UE are transmitted, preferably the DCI is transmitted        in the UE-specific search space.

As a variant of the embodiment, instead of including one or more of theabove contents into the FRI, one or more of the above could be used todetermine the RE(s) where the FRI is transmitted. For example, the HARQprocess could determine the RE(s) where the FRI is transmitted. A UEwould then monitor multiple FRI resources and preferably evaluates onlythe FRI that is received with the strongest power.

As described with respect to the several variants of the embodimentabove, a positive FRI would not imply an implicit or explicit change ofthe RV for the retransmission, in contrast to retransmissions triggeredby HI described in the background section. However, as a further variantof the embodiment, a retransmission triggered by an FRI should notaffect a potential RV determination rule for non-adaptiveretransmissions by PHICH. As indicated previously in the backgroundsection, a retransmission triggered by PHICH implicitly cyclicallyswitches between RV {0, 2, 3, 1}. According to this variant, a positiveFRI should be ignored for purposes of RV determination for laternon-adaptive retransmissions, i.e., the RV switching/cycling should onlytake the RV of previous DCI/HI-triggered (re-)transmissions intoaccount.

As a further variant of the embodiment, in addition to using the FRI asdescribed above, in case the PUSCH occupies not a full 1 ms TTI, but ashort TTI (as being discussed in the Short Latency study item above),the transport blocks are smaller than in a 1 ms TTI, so that thedecoding result (OK/failure) at the eNodeB would be available sooner.Hence, in this case, the FRI could be transmitted earlier than a DCI/HIin a conventional system.

As another implementation of the embodiment, a previous transmission ofthe data packet may be an “initial transmission of the data packet” or a“retransmission of the data packet.”

Hardware and Software Implementation of the Present Disclosure

Other exemplary embodiments relate to the implementation of the abovedescribed various embodiments using hardware, software, or software incooperation with hardware. In this connection a user equipment (mobileterminal) is provided. The user equipment is adapted to perform themethods described herein, including corresponding entities toparticipate appropriately in the methods, such as receiver, transmitter,processors.

It is further recognized that the various embodiments may be implementedor performed using computing devices (processors). A computing device orprocessor may for example be general purpose processors, digital signalprocessors (DSP), application specific integrated circuits (ASIC), fieldprogrammable gate arrays (FPGA) or other programmable logic devices,etc. The various embodiments may also be performed or embodied by acombination of these devices. In particular, each functional block usedin the description of each embodiment described above can be realized byan LSI as an integrated circuit. They may be individually formed aschips, or one chip may be formed so as to include a part or all of thefunctional blocks. They may include a data input and output coupledthereto. The LSI here may be referred to as an IC, a system LSI, a superLSI, or an ultra LSI depending on a difference in the degree ofintegration. However, the technique of implementing an integratedcircuit is not limited to the LSI and may be realized by using adedicated circuit or a general-purpose processor. In addition, a FPGA(Field Programmable Gate Array) that can be programmed after themanufacture of the LSI or a reconfigurable processor in which theconnections and the settings of circuits cells disposed inside the LSIcan be reconfigured may be used.

Further, the various embodiments may also be implemented by means ofsoftware modules, which are executed by a processor or directly inhardware. Also a combination of software modules and a hardwareimplementation may be possible. The software modules may be stored onany kind of computer readable storage media, for example RAM, EPROM,EEPROM, flash memory, registers, hard disks, CD-ROM, DVD, etc. It shouldbe further noted that the individual features of the differentembodiments may individually or in arbitrary combination be subjectmatter to another embodiment.

It would be appreciated by a person skilled in the art that numerousvariations and/or modifications may be made to the present disclosure asshown in the specific embodiments. The present embodiments are,therefore, to be considered in all respects to be illustrative and notrestrictive.

The various embodiments described above can be combined to providefurther embodiments. All of the U.S. patents, U.S. patent applicationpublications, U.S. patent applications, foreign patents, foreign patentapplications and non-patent publications referred to in thisspecification and/or listed in the Application Data Sheet areincorporated herein by reference, in their entirety. Aspects of theembodiments can be modified, if necessary to employ concepts of thevarious patents, applications and publications to provide yet furtherembodiments.

These and other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

The invention claimed is:
 1. An integrated circuit which, in operation,controls a process of a user equipment operating a transmission protocolfor uplink data packet transmission in a communication system, theprocess comprising: receiving a Fast Retransmission Indicator (FM),wherein the FRI indicates that a base station requests a retransmissionof a previously-transmitted data packet using identical transmissionparameters as the previously-transmitted data packet; and retransmittingthe data packet using the identical transmission parameters as used forthe previously-transmitted data packet.
 2. The integrated circuitaccording to claim 1, wherein the FRI indicates that the retransmissionis to be performed with an identical redundancy version as used for thepreviously-transmitted data packet, and wherein the integrated circuitis further operative to use the identical redundancy version as thepreviously-transmitted data packet for retransmitting the data packet.3. The integrated circuit according to claim 2, wherein the identicaltransmission parameters include a scrambling code of thepreviously-transmitted data packet.
 4. The integrated circuit accordingto claim 1, wherein the FRI indicates that a retransmission of a part ofthe previously-transmitted data packet is to be performed, and whereinthe integrated circuit is further operative to cause the indicated partof the previously-transmitted data packet to be retransmitted.
 5. Theintegrated circuit according to claim 4, wherein the retransmissionfurther uses a transmit power for the retransmission of the part of thepreviously transmitted data packet such that a total transmit power forthe retransmission equals a total transmit power of the previouslytransmitted data packet.
 6. The integrated circuit according to claim 5,wherein using 50% of the data packet results in a transmission powerincrease of the part of the previously-transmitted data packet by afactor
 2. 7. The integrated circuit according to claim 4, wherein thepart of the previously-transmitted data packet is 50% or 25% of thepreviously-transmitted data packet.
 8. The integrated circuit accordingto claim 1, wherein receiving the FRI includes receiving the FRI at afirst timing after the transmission of the previously-transmitted datapacket, wherein the first timing is fixed or semi-staticallyconfigurable by the base station.
 9. The integrated circuit according toclaim 1, wherein the data packet is retransmitted at a second timingafter receiving the FM, and wherein the second timing is fixed,semi-static configurable by the base station, or variable based on arespective information included in the received FRI.
 10. The integratedcircuit according to claim 1, wherein the retransmission of the datapacket is triggered by a Downlink Control Information (DCI) or a HARQIndicator (HI), and wherein a first time period between the previoustransmission of the data packet and the reception of the FM, or a secondtime period between the reception of the FRI and the retransmission ofthe data packet is smaller than a third time period between reception ofthe DCI or HI and its corresponding retransmission of the data packet,wherein at least one of the first and second time periods is smallerthan 4 ms.
 11. The integrated circuit according to claim 10, wherein incase that a request for performing the retransmission of the data packetby the FRI is received and a request for performing, at the same time,transmission of another data packet by the DCI or HI, the integratedcircuit is further operative to follow the request by the FRI and toignore the request by the DCI or HI.
 12. The integrated circuitaccording to claim 1, wherein the FRI further comprises a HARQ processnumber indicator for indicating a HARQ process that was used by theintegrated circuit for the previous transmission of the data packet. 13.The integrated circuit according to claim 1, wherein the previoustransmission of the data packet is an initial transmission or aretransmission of the data packet.
 14. The integrated circuit accordingto claim 1, wherein the FRI is received in radio resources used forreceiving an HI the FRI is received as a DCI, the FRI is received inpreconfigured radio resources of a common search space or the FRI isreceived in preconfigured radio resources of a user-equipment-specificsearch space.
 15. The integrated circuit according to claim 1, whereinwhen the user equipment uses multiple transmitting antennas fortransmission of data packets: receiving the FRI triggers aretransmission of the data packets, and the retransmission includesretransmitting the data packets to the base station using the multipletransmitting antennas; or receiving the FRI triggers a retransmission ofone of the data packets, and the retransmission includes retransmittingthe one of the data packets to the base station using the multipletransmitting antennas.